ENV4106 Irrigation Science – University of Southern Queensland
Crop Evapotranspiration and Irrigation Scheduling Assignment
Using the daily meteorological data contained in the text file provided on StudyDesk, develop a daily soil-water balance, and prepare and evaluate an irrigation schedule for the crop and soil conditions listed below.
Present your software calculations and your explanation and evaluation in a comprehensive and properly structured report which should include at least:
1. An evaluation of the evaporation estimation technique you have developed, both as regards convenience of use, and likely accuracy. This should include a description of the processes that you have put in place to deal with missing meteorological data;
2. A sensitivity analysis to determine the influence of the various input parameters on the ETc values and on the depth of irrigation applied over the crop cycle. Input parameters considered in this analysis should be the key meteorological variables and crop parameters.
3. A discussion of the irrigation strategy including:
• a plot (daily) of the depth of available soil moisture in the form of a “saw-tooth” shaped curve with soil moisture on the Y-axis and time on the X-axis, and
• total depths of irrigation water applied and effective rainfall.
4. All important and salient graphs, correctly generated, appropriately labelled, and captioned.
To calculate the crop evaporation for this site, and design an irrigation schedule for your chosen summer crop, you will :
• use the FAO Penman Monteith equation as described by Eqn 6 in Chapter 2 of the FAO Irrigation and Drainage Paper 56 (Allen et al., 1998),
• understand the major meteorological variables from Chapter 3 of Allen et al (1998) and how to deal with missing values of these,
• use the daily time step process described in Chapter 4 of Allen et al (1998) to calculate reference crop evaporation, ET0,
• use the single crop coefficient method, and the associated crop factors, Kc, from Chapter 6 to determine crop evapotranspiration, ETc, and
• sum all components of the water balance to generate a daily soil water content that you can describe and plot.
The process in your software/spreadsheet will include, as appropriate:
• Pre-processing of the meteorological data by the developed software, with automated processing of missing data;
• ET0 calculation;
• Estimation of Kc (crop type and stage, using single coefficients only);
• Kc adjustment appropriate for single crop coefficient;
• ETc calculation; and
• Application of a daily water balance.
Crop and Soil Data:
Location Griffith, Southern Central NSW, Latit. -34.25°, Long. 146.07°, Elevation of station: 134.0 m, Elevation of barometer: 135 m
Crop Annual summer crop (field or row crop) of your choice Planting Date Between 1st Sep. and 1st Feb.
Soil Moisture Content at Saturation 0.37 m3/m3 Soil Moisture Content at Field Capacity 0.32 m3/m3 Soil Moisture (one month prior to planting) 0.25 m3/m3 Maximum Soil Moisture Deficit 70 mm